Geographical areas served by Public Land Mobile Networks (PLMNs) are typically partitioned into mobility areas (MAs) which may be referred to as, for example, location areas (LAs), routing areas (RAs) or tracking areas (TAs). A set of mobility areas managed by one or more network nodes is known as the service area (SA) for these nodes. The purpose of these areas is to keep an approximate track of the whereabouts of user equipments (UEs) in the PLMNs.
The design of these areas reflects a trade off between the need for position updating (i.e. UEs updating the network about changes in their MA) and user paging (i.e. networks locating UEs when there is incoming traffic to a UE). The larger the area, the less resources have to be spent on position updating in the network (i.e. reduced need for MA updates) since large areas means that it is less likely that users leave the area to which they are associated. However, more resources instead have to be spent on user paging in the network (i.e. increased need for pages) since large areas also means that users typically must be paged in more cells.
The second and third generations of mobile systems (2G and 3G, also referred to as GSM and WCDMA respectively) use a “double” partitioning, that is, LAs for circuit switched services and RAs for packet switched services. Mobile Switching Centres/Visited Location Registers (MSC/VLRs) which manage circuit switched traffic, keep track of the LAs of all UEs in their respective SAs while Serving GPRS Service Nodes (SGSNs), which manage packet switched traffic, keep track of the RAs of all UEs in their respective SAs. A problem with this solution is that it is inflexible in the sense that all users, irrespective of how mobile they are, must be handled in the same way. This means, for example, that those users who do not move at all are often paged in large areas in spite of their immobility and/or that those users who move quickly must update their LAs and RAs continuously and frequently.
The fourth generation of mobile systems (4G, also referred to as LTE), which only handles packet switched traffic, uses single partitioning into TAs and Mobility Management Entities (MMEs) keep track of the TAs of all UEs in their respective SAs. TAs are identified by numbers (TAIs) and collections of TAIs are known as TAI lists. TAI lists increase the flexibility compared to 2G and 3G in that UEs can be assigned TAI lists, and thus be registered in multiple TAs. It is noted that, although the use of TAI lists in 4G mobile systems introduces a degree of flexibility compared to the rigid LAs and RAs in 2G and 3G mobile systems, this does not solve the problem of optimising the trade-off between position updating and user paging. The problem of position updating is more or less the same as in 2G and 3G mobile systems wherein typically solutions include management concerns with respect to administrative boundaries, load concerns with respect to MSCs and SGSNs, and combinations of experience and intuition. However, this problem is not referred to in any more detail herein. Instead, focus is on the problem of performing the user paging.
WO/2008/112161 and WO/2008/146868 describe the use of TAI lists. The common denominators are that they both suggest that (i) different TAI lists be applied for different degrees of mobility such as no movement, slow movement and fast movement and that (ii) UEs are supposed to explicitly detect and report such states to MMEs or similar entities. These solutions, however, require modifications in the UEs which are very difficult to implement given the large numbers of users and UEs involved. Furthermore, TAI lists for users with fast movements may include large numbers of TAs in which user paging still may be inefficient, or that “artificial” limits may have to be imposed on these TAI lists in order to perform efficient user paging.
WO/2008/031269 describes a solution which seems to be directed towards reducing the number of paging attempts. WO/2008/031269 apply mainly to 2G and 3G mobile systems and attempt to reduce the number of cells in which a user is paged by not paging in the entire LA/RA but in the cell where the user was most recently seen and possibly also in a set of neighbouring cells as extracted from databases.
WO/2008/031269 seems to describe automatic insertion and removal of suitable cells from such paging sets of cells based on observed paging success rates, and also deals with further aspects as to which cells to include in this list of cells. The solution is limited in that users assigned long TAI lists will be observed less frequently, hence the last observation of the user may be older and thus less relevant. In other words, these solutions make it difficult to take full advantage of TAI lists and, in particular, to combine position reporting efficiency with performing efficient user paging.
In the Master Thesis, “Dynamic Location Management and Activity-based Mobility Modelling for Cellular Networks” (John Scourias, Master Thesis, University of Waterloo, (1997)), a solution is proposed in which UEs collect statistics on cell changes (per cell pair) and cell camping times (per cell) and that the results be used to select a paging area of cells and a cell paging order. The paging area of cells is created by adding the current cell to an empty list and repeatedly including the most likely next cells for all cells in the list based on the cell change statistics. The list is formed by the UE and then reported to the network. The paging order of cells is created by paging in the cells with the longest average camping times first and paging in the cells with the shortest average camping times last. However, this solution requires that the UEs collect statistics, compute paging areas of cells and report the results to the network. Notwithstanding the required modifications to the UEs to perform these tasks, it will also increase UE power consumption. Moreover, it will create more control signalling to take place in the network, which will increase the load on network elements and signalling channels.
Additionally, this solution also does not take current information or regular movement patterns of UEs into account. In general, this solution provides a conflict between saving location updates and saving paging attempts. Few location updates are obtained from comprehensive lists but such lists may cause more paging attempts as average camping times become less relevant as location predictors over longer time scales.